Preclinical and clinical results with the natural marine product ET-743

ET-743 (Yondelis, trabectedin) is a natural marine product with antitumour properties derived from the tunicate Ecteinascidia turbinata. ET-743 binds to the N2 position of guanine in the minor groove of DNA with some degree of sequence specificity, altering the transcription regulation of induced genes. Cells that are deficient in nucleotide excision repair, hypersensitive to UV rays, cisplatin and conventional alkylating agents, are resistant to ET-743. This is a unique property of ET-743 and is of potential importance for the drug activity when administered alone or in combination with other drugs. ET-743 showed striking antitumour activity against sensitive and resistant human xenografts. The dose-limiting toxicities in animal models, hepatobiliary events, were of concern, but the pattern of the reversibility noted in monkeys and the evidence of a positive therapeutic index in tumour-bearing nude mice prompted its clinical development. The Phase I programme investigated different schedules of administration, with the dose-limiting toxicities being neutropenia and fatigue. As anticipated in the preclinical models, reversible non-cumulative transaminitis was a prevalent finding from one-third of the maximum tolerated dose level; long-lasting objective responses in pretreated resistant patients were noted, including consistent efficacy data in mesenchymal tumours. The Phase II data for ET-743 administered as a single agent has established a clinical role for the compound in advanced pretreated soft tissue sarcoma and a promising potential in pretreated ovarian and breast cancer. ET-743 combined with other drugs (i.e., cisplatin, paclitaxel or doxorubicin) showed more than additive effects in several preclinical systems and initial clinical results (e.g., a combination of ET-743 with cisplatin) appear to confirm the preclinical findings. In summary, ET-743 is a new drug with a novel mode of action, which has demonstrated activity in human tumours resistant to the available anticancer drugs. Further comparative studies are needed to define the role of ET-743 alone or in combination in cancer chemotherapy.